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5.8 Diesel Fuel Water Separator

The diesel models covered by this manual (except some 1985 Golf Diesels) are equipped with an in-line water separator between the fuel tank and the diesel injection pump. The separator collects the water that it separates from the fuel, and it must be periodically drained. Under normal use with good quality fuel, the specified maintenance interval is sufficient, however, a blinking glow plug light also indicates that the water separator should be drained. If the light blinks again within a few miles after draining, the fuel is most likely contaminated, and the fuel tank should be flushed.


Diesel fuel is damaging to rubber. Immediately wipe up any fuel that spills on belts or hoses. Extreme cleanliness should be observed when working on the diesel fuel system. Even the smallest particle of dirt may damage the system.

To drain water from the water separator, use the drain hose and plastic bag supplied with the car. Attach the hose to the drain valve outlet, route it to the plastic bag, as shown in Fig. 5-9. If the original hose is not available, use a piece of clear hose approximately 300 mm (12 in.) long and a suitable container. Open the separator drain valve (three turns maximum) and let the fluid drain until clear fuel enters the hose. Close the drain valve and remove the hose. Disconnect it from the water separator first. If the water separator is being drained because the glow plug light was blinking, then the fuel filter should also be drained as described in Draining Water From Diesel Fuel Filter.

Fig. 5-4 Diesel fuel water separator, located in front of right rear wheel. When draining, open valve a maximum of three turns (top arrows), and drain until fuel is clear. Lower arrow indicates valve on drain hose.

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